Like it or not, you will have to either

a) reinstall Windows


b) buy a new system

Either way you will have to spend another week and a half setting it up. Option (a) saves money, since it seems there is really nothing wrong with the PC.

Unfortunately there is no way to do this without expending any effort. No-one likes to be told that, but they all know it to be the case. You should have a better backup strategy so that if this happens you can quickly restore and get under way again (no-one likes to be told that either). RAID is not a backup strategy. Supposedly having a backup "but who knows?" is also not a backup strategy.

There are a few things you can do to get back to where you were. First, check the RAM. A good way to do this is with the free 'memtest' software. A good way to get this is to get hold of a Linux live CD such as Ubuntu or Mepis (or make your own bootable CD with only memtest on it). Run it overnight and see what it comes up with. Next, the quickest solution I can see is to just start using the new Windows install that you made. It works, so just add all the bits that are missing. Another thing, have you tried rolling back the drivers to a previous state? You might have to boot XP into safe mode, but I have never needed to do this, so I don't know the procedure. These days I run Linux.